U.S. patent number 10,118,121 [Application Number 15/248,168] was granted by the patent office on 2018-11-06 for plugged honeycomb structure and plugged honeycomb segment.
This patent grant is currently assigned to NGK Insulators, Ltd.. The grantee listed for this patent is NGK INSULATORS, LTD.. Invention is credited to Toshihiro Hirakawa, Kazuya Mori.
United States Patent |
10,118,121 |
Mori , et al. |
November 6, 2018 |
Plugged honeycomb structure and plugged honeycomb segment
Abstract
A plugged honeycomb structure includes: a plurality of honeycomb
segments, a bonding layer, and plugging portions to plug open ends
of cells of the honeycomb segments. The honeycomb segment is
configured so that the cells having at least two kinds of different
shapes are disposed in a cross section orthogonal to an extension
direction of the cells, the honeycomb segment has a center region
configured by repeating units to maintain a repeated pattern
including cell arrangement in which inflow cells surround an inflow
cell, and a circumferential region located at the circumference of
the center region, the circumferential region has open frontal area
that is larger than open frontal area of the center region at the
inflow end face of the honeycomb segment, the segment
circumferential wall and the bonding layer have a special range of
a thickness.
Inventors: |
Mori; Kazuya (Nagoya,
JP), Hirakawa; Toshihiro (Nagoya, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
NGK INSULATORS, LTD. |
Nagoya |
N/A |
JP |
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Assignee: |
NGK Insulators, Ltd. (Nagoya,
JP)
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Family
ID: |
58011414 |
Appl.
No.: |
15/248,168 |
Filed: |
August 26, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170056805 A1 |
Mar 2, 2017 |
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Foreign Application Priority Data
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Sep 2, 2015 [JP] |
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2015-172708 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D
46/2459 (20130101); B01D 46/2474 (20130101); B01D
46/247 (20130101); B01D 46/2455 (20130101); B01D
46/2466 (20130101); B01D 2046/2492 (20130101); B01D
2046/2481 (20130101); B01D 2046/2485 (20130101) |
Current International
Class: |
B01D
50/00 (20060101); B01D 46/24 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2014-200741 |
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Oct 2014 |
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JP |
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2015-029939 |
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Feb 2015 |
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JP |
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Primary Examiner: Orlando; Amber R
Attorney, Agent or Firm: Burr & Brown, PLLC
Claims
What is claimed is:
1. A plugged honeycomb structure, comprising: a plurality of
prismatic-columnar shaped honeycomb segments, each having porous
partition walls that define a plurality of cells extending from an
inflow end face to which a fluid flows to an outflow end face from
which a fluid flows, and a segment circumferential wall disposed at
an outermost circumference of each of the honeycomb segments; a
bonding layer to bond the side surfaces of the plurality of
honeycomb segments; and plugging portions disposed in open ends of
predetermined cells in the inflow end face of each of the honeycomb
segments and in open ends of residual cells in the outflow end face
of each of the honeycomb segments, wherein each of the honeycomb
segments is configured so that the cells having at least two kinds
of different shapes are disposed in a cross section orthogonal to
an extension direction of the cells, each of the honeycomb segments
has a center region including a center of the cross section
orthogonal to the extension direction of the cells and a
circumferential region located on the side of the circumference of
the center region, the center region of each of the honeycomb
segments has a repeated pattern of repeating units including a cell
arrangement in which inflow cells in which the plugging portions
are disposed in open ends of the cells in the outflow end face
surround one outflow cell in which the plugging portions are
disposed in open ends of the cell in the inflow end face and the
inflow cells are substantially the same size, in the inflow end
face of at least one of the honeycomb segments, the circumferential
region is configured to have an open frontal area that is larger
than an open frontal area of the center region, a thickness of the
segment circumferential wall of each of the honeycomb segments is
from 0.3 to 1.0 mm, and a thickness of the bonding layer is from
0.5 to 1.5 mm.
2. The plugged honeycomb structure according to claim 1, wherein
the repeated pattern includes the cells having at least two kinds
of different shapes.
3. The plugged honeycomb structure according to claim 1, wherein
center region cells disposed in the center region include two kinds
or more of the cells that are different in shape of the cross
section.
4. The plugged honeycomb structure according to claim 1, wherein a
value obtained by subtracting a value of an open frontal area in
the center region from a value of an open frontal area in the
circumferential region is 10% or more.
5. A plugged honeycomb segment, comprising: a prismatic-columnar
shaped honeycomb segment having porous partition walls that define
a plurality of cells extending from an inflow end face to which a
fluid flows to an outflow end face from which a fluid flows, and a
segment circumferential wall disposed at an outermost circumference
of each of the honeycomb segments; and plugging portions disposed
in open ends of predetermined cells in the inflow end face of each
of the honeycomb segments and in open ends of residual cells in the
outflow end face of each of the honeycomb segments, wherein each of
the honeycomb segments is configured so that the cells having at
least two kinds of different shapes are disposed in a cross section
orthogonal to an extension direction of the cells, each of the
honeycomb segments has a center region including a center of the
cross section orthogonal to the extension direction of the cells
and a circumferential region located on the side of the
circumference of the center region, in the center region each of
the honeycomb segments has a repeated pattern of repeating units
including a cell arrangement in which inflow cells in which the
plugging portions are disposed in open ends of the cells in the
outflow end face surround one outflow cell in which the plugging
portions are disposed in open ends of the cell in the inflow end
face and the inflow cells are substantially the same size, in the
inflow end face of the honeycomb segment, the circumferential
region is configured to have an open frontal area that is larger
than an open frontal area of the center region, and a thickness of
the segment circumferential wall of each of the honeycomb segments
is from 0.3 to 1.0 mm.
6. The plugged honeycomb segment according to claim 5, wherein the
repeated pattern includes the cells having at least two kinds of
different shapes.
7. The plugged honeycomb segment according to claim 5, wherein
central region cells disposed in the center region include two
kinds or more of the cells that are different in shape of the cross
section.
8. The plugged honeycomb segment according to claim 5, wherein a
value obtained by subtracting a value of an open frontal area in
the center region from a value of an open frontal area in the
circumferential region is 10% or more.
Description
The present application is an application based on JP2015-172708
filed on Feb. 9, 2015 with the Japan Patent Office, the entire
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a plugged honeycomb structure and
a plugged honeycomb segment. More particularly the present
invention relates to a plugged honeycomb structure and a plugged
honeycomb segment capable of improving a continuous regeneration
performance of a filter to trap a particulate matter when they are
used as the filter and so preventing a segregation of a particulate
matter in the filter.
Description of the Related Art
In recent years, there has been a demand for the reduction in a
fuel consumption of an automobile from the viewpoints of influences
on the global environment and resource saving. This leads to a
tendency of using internal combustion engines with a good thermal
efficiency, such as a direct injection type gasoline engine and a
diesel engine, as a power source for an automobile.
Meanwhile, these internal combustion engines have a problem that a
soot is generated during a combustion of the fuel. A countermeasure
has been then required from the viewpoint of an air environment to
remove toxic components included in an exhaust gas and to avoid the
emission of a particulate matter (hereinafter this may be called "a
PM"), such as a soot or an ash, to the air.
Especially there is a global tendency of tightening the regulations
on a removal of the PM emitted from a diesel engine. Then a
honeycomb-structured wall flow type exhaust gas purification filter
has attracted the attention as a trapping filter (this may be
called a "DPF") to remove the PM, and various systems for the
filter have been proposed. Such a DPF is typically configured so
that a plurality of cells serving as a through channel of a fluid
is defined by a porous partition wall, and by plugging the cells
alternately, the porous partition wall making up the cells
functions as a filter. A pillar-shaped structure including a
plurality of cells defined by a porous partition wall may be called
a "honeycomb structure". Then a honeycomb structure including cells
whose open ends are plugged with plugging portions may be called a
"plugged honeycomb structure". A plugged honeycomb structure is
widely used as a trapping filter, such as a DPF. As an exhaust gas
containing a particulate matter flows into the plugged honeycomb
structure from the inflow end face (first end face) of the plugged
honeycomb structure, the particulate matter in the exhaust gas is
filtered when the exhaust gas passes through the partition wall,
and the purified gas is emitted from the outflow end face (second
end face) of the plugged honeycomb structure.
Conventionally a plugged honeycomb structure includes the cells,
such as quadrangular cells, hexagonal cells, and HAC cells (cells
having the geometry that is the combination of octagons and
quadrangles). Recently new plugged honeycomb structures which
include the combination of cells of different shapes or devise the
position of plugging have been developed (see Patent Documents 1
and 2). Such plugged honeycomb structures allow a pressure loss at
the initial stage of use to be reduced, and allow a pressure loss
when a PM is accumulated to be reduced, and then allow cracks
during burning of the PM to be suppressed and a lot of ash at the
partition wall to be accumulated.
[Patent Document 1] JP-A-2014-200741
[Patent Document 2] JP-A-2015-029939
SUMMARY OF THE INVENTION
When a plugged honeycomb structure having a special shape of cells
as shown in Patent Documents 1 and 2 is provided as a DPF in an
internal combustion engine of an automobile or the like, such a
plugged honeycomb structure typically is manufactured to have a
round pillar shape of a certain size. The following manufacturing
method is proposed as one of the methods to manufacture a round
pillar-shaped plugged honeycomb structure. Firstly, a plurality of
honeycomb segments, which has partition walls to form special cells
(having a special shape) and a segment circumferential wall to
surround the circumference of the special cells, is prepared. Next,
the plurality of honeycomb segments are bonded with a bonding
material to prepare a bonded member of the honeycomb segments
(hereinafter called a "honeycomb-segment bonded member"). Next, the
circumference of the honeycomb-segment bonded member is ground into
an arbitrary shape, and then the circumference is subjected to a
coating treatment to manufacture a plugged honeycomb structure.
Hereinafter a plugged honeycomb structure manufactured by such a
method may be called a "plugged honeycomb structure having a
segmented structure".
Such a plugged honeycomb structure having a segmented structure may
be used as a trapping filter to purify an exhaust gas emitted from
a gasoline engine (typically a direct injection type gasoline
engine). Note here that the temperature of an exhaust gas emitted
from gasoline engines is typically higher than the temperature of
an exhaust gas emitted from diesel engines. Therefore it is
important for a trapping filter to purify an exhaust gas emitted
from a gasoline engine to have a continuous regeneration
performance so as to burn the collected the PM while the filter is
collecting the PM. Less an exhaust gas flows through the
circumferential part of each of the honeycomb segments of a plugged
honeycomb structure having a segmented structure, which means that
the amount of the PM trapped at the circumferential part becomes
less than that at the center part. However, since less an exhaust
gas at high temperatures also flows at the circumferential part of
each of the honeycomb segments, the continuous regeneration
performance as described above deteriorates, and more PM tends to
be accumulated at the circumferential part of each of the honeycomb
segments by purifying an exhaust-gas for a long time. If the PM is
accumulated excessively at the circumferential part only, the
excessively accumulated PM is burnt suddenly and the honeycomb
segment may break in some cases.
In view of such problems of the conventional techniques, the
present invention provides a plugged honeycomb structure capable of
improving a continuous regeneration performance of a filter to trap
a particulate matter when it is used as the filter and so
preventing a segregation of a particulate matter in the filter, and
such a plugged honeycomb segment.
As a result of further investigations to solve the aforementioned
problems, the present inventors obtained the following findings. It
was found that, in a honeycomb segment having a specific cell
arrangement, devising a shape of the honeycomb segment on the side
of the circumference allows the continuous regeneration performance
of the plugged honeycomb structure to be improved. That is, an open
frontal area in the circumferential region of the honeycomb segment
is made larger than an open frontal area in the center region
without changing the cell shape of each of the honeycomb segments
itself. It was found that, with this configuration, a continuous
regeneration performance of the plugged honeycomb structure can be
improved, and a segregation of a particulate matter in the filter
can be suppressed. The present invention provides the following
plugged honeycomb structure and plugged honeycomb segment.
According to a first aspect of the present invention, a plugged
honeycomb structure is provided, comprising:
a plurality of prismatic-columnar shaped honeycomb segments, each
having porous partition walls that define a plurality of cells
extending from an inflow end face to which a fluid flows to an
outflow end face from which a fluid flows, and a segment
circumferential wall disposed at an outermost circumference of each
of the honeycomb segments;
a bonding layer to bond the side surfaces of the plurality of
honeycomb segments; and
plugging portions disposed in open ends of predetermined cells in
the inflow end face of each of the honeycomb segments and in open
ends of residual cells in the outflow end face of each of the
honeycomb segments, wherein
each of the honeycomb segments is configured so that the cells
having at least two kinds of different shapes are disposed in a
cross section orthogonal to an extension direction of the
cells,
each of the honeycomb segments has a center region including a
center of the cross section orthogonal to the extension direction
of the cells and a circumferential region located in the side of
the circumference of the center region,
each of the honeycomb segments has a repeated pattern including
cell arrangement in which inflow cells in which the plugging
portions are disposed in open ends of the cells in the outflow end
face surround one outflow cell in which the plugging portions are
disposed in open ends of the cell in the inflow end face, and a
range including repeating units to maintain the repeated pattern is
the center region,
in the inflow end face of at least one of the honeycomb segments,
the circumferential region is configured to have an open frontal
area that is larger than an open frontal area of the center
region,
a thickness of the segment circumferential wall of each of the
honeycomb segments is from 0.3 to 1.0 mm, and
a thickness of the bonding layer is from 0.5 to 1.5 mm.
According to a second aspect of the present invention, the plugged
honeycomb structure according to above first aspect is provided,
wherein the repeated pattern includes the cells having at least two
kinds of different shapes.
According to a third aspect of the present invention, the plugged
honeycomb structure according to above first or second aspects is
provided, wherein center region cells disposed in the center region
include two kinds or more of the cells that are different in shape
of the cross section.
According to a fourth aspect of the present invention, the plugged
honeycomb structure according to any one of above first to third
aspects is provided, wherein a value obtained by subtracting a
value of an open frontal area in the center region from a value of
an open frontal area in the circumferential region is 10% or
more.
According to a fifth aspect of the present invention, a plugged
honeycomb segment is provided, comprising:
a prismatic-columnar shaped honeycomb segment having porous
partition walls that define a plurality of cells extending from an
inflow end face to which a fluid flows to an outflow end face from
which a fluid flows, and a segment circumferential wall disposed at
an outermost circumference of each of the honeycomb segments;
and
plugging portions disposed in open ends of predetermined cells in
the inflow end face of each of the honeycomb segments and in open
ends of residual cells in the outflow end face of each of the
honeycomb segments, wherein
each of the honeycomb segments is configured so that the cells
having at least two kinds of different shapes are disposed in a
cross section orthogonal to an extension direction of the
cells,
each of the honeycomb segments has a center region including a
center of the cross section orthogonal to the extension direction
of the cells and a circumferential region located in the side of
the circumference of the center region,
each of the honeycomb segments has a repeated pattern including
cell arrangement in which inflow cells in which the plugging
portions are disposed in open ends of the cells in the outflow end
face surround one outflow cell in which the plugging portions are
disposed in open ends of the cell in the inflow end face, and a
range including repeating units to maintain the repeated pattern is
the center region,
in the inflow end face of the honeycomb segment, the
circumferential region is configured to have an open frontal area
that is larger than an open frontal area of the center region,
and
a thickness of the segment circumferential wall of each of the
honeycomb segments is from 0.3 to 1.0 mm.
According to a sixth aspect of the present invention, the plugged
honeycomb segment according to above fifth aspect is provided,
wherein the repeated pattern includes the cells having at least two
kinds of different shapes.
According to a seventh aspect of the present invention, the plugged
honeycomb segment according to above fifth or sixth aspects is
provided, wherein center region cells disposed in the center region
include two kinds or more of the cells that are different in shape
of the cross section.
According to an eighth aspect of the present invention, the plugged
honeycomb segment according to any one of above fifth to seventh
aspects is provided, wherein a value obtained by subtracting a
value of an open frontal area in the center region from a value of
an open frontal area in the circumferential region is 10% or
more.
A plugged honeycomb structure of the present invention is a
so-called plugged honeycomb structure having a segmented structure,
in which the center region of the honeycomb segment includes the
range configured by repeating units to maintain a repeated pattern
including a specific cell arrangement. In the plugged honeycomb
structure of the present invention, in the inflow end face of the
honeycomb segment, the circumferential region is configured to have
an open frontal area that is larger than an open frontal area of
the center region. In the plugged honeycomb structure of the
present invention, a thickness of the segment circumferential wall
of each of the honeycomb segments is from 0.3 to 1.0 mm, and a
thickness of the bonding layer is from 0.5 to 1.5 mm. The thus
configured plugged honeycomb structure can improve a continuous
regeneration performance of a filter to trap a particulate matter
when it is used as the filter and prevent a segregation of a
particulate matter in the filter.
A plugged honeycomb segment of the present invention is to
manufacture a plugged honeycomb structure of the present invention.
A plurality of the plugged honeycomb segments of the present
invention is used and the side surfaces of the plurality of
honeycomb segments are bonded to each other via bonding layer,
whereby a plugged honeycomb structure of the present invention can
be manufactured very simply.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic perspective view showing the first embodiment
of a plugged honeycomb structure according to the present invention
when viewed from its inflow-side end face.
FIG. 2 is a schematic plan view showing the first embodiment of the
plugged honeycomb structure according to the present invention when
viewed from its inflow-side end face.
FIG. 3 is an enlarged plan view of a part of the inflow end face of
the plugged honeycomb structure shown in FIG. 2.
FIG. 4 is an enlarged plan view of a part of the outflow end face
of the plugged honeycomb structure shown in FIG. 2.
FIG. 5 is a schematic cross-sectional view taken along the line
A-A' of FIG. 3.
FIG. 6 is a schematic perspective view showing a plugged honeycomb
segment included in the plugged honeycomb structure shown in FIG. 1
when viewed from the inflow-side end face.
FIG. 7 is a schematic plan view showing the plugged honeycomb
segment included in the plugged honeycomb structure shown in FIG. 1
when viewed from the inflow-side end face.
FIG. 8 is a schematic plan view showing the plugged honeycomb
segment included in the plugged honeycomb structure shown in FIG. 1
when viewed from the outflow-side end face.
FIG. 9 is a schematic partially enlarged view showing the first
embodiment of the plugged honeycomb structure according to the
present invention when viewed from the inflow-side end face.
FIG. 10 is a schematic plan view showing a plugged honeycomb
segment included in the second embodiment of a plugged honeycomb
structure according to the present invention when viewed from the
inflow-side end face.
FIG. 11 is a schematic plan view showing a plugged honeycomb
segment included in the third embodiment of a plugged honeycomb
structure according to the present invention when viewed from the
inflow-side end face.
FIG. 12 is a schematic plan view showing a plugged honeycomb
segment included in the fourth embodiment of a plugged honeycomb
structure according to the present invention when viewed from the
inflow-side end face.
FIG. 13 is a schematic plan view showing a plugged honeycomb
segment included in the fifth embodiment of a plugged honeycomb
structure according to the present invention when viewed from the
inflow-side end face.
FIG. 14 is a schematic partially enlarged plan view showing a
plugged honeycomb segment included in the sixth embodiment of a
plugged honeycomb structure according to the present invention when
viewed from the inflow-side end face.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, embodiments of the present invention will be
described. The present invention is not limited to the embodiments
below, and the embodiments below can be, of course, appropriately
modified and improved based on the general knowledge of the person
skilled in the art without departing from the spirit of the present
invention. Then, these modifications and improvements are also
included in the scope of the present invention.
(1) Plugged Honeycomb Structure:
As shown in FIGS. 1 through 5, a plugged honeycomb structure of the
first embodiment of the present invention is a plugged honeycomb
structure 100 that includes a plurality of honeycomb segments 4, a
bonding layer 6, and plugging portions 5. That is, the plugged
honeycomb structure 100 according to the present embodiment is a
so-called plugged honeycomb structure having a segmented structure.
The plugged honeycomb structure 100 further includes an outer wall
8 in the circumference so as to surround the plurality of honeycomb
segments 4.
Herein, FIG. 1 is a schematic perspective view showing the first
embodiment of a plugged honeycomb structure according to the
present invention when viewed from its inflow-side end face. FIG. 2
is a schematic plan view showing the first embodiment of the
plugged honeycomb structure according to the present invention when
viewed from its inflow-side end face. FIG. 3 is an enlarged plan
view of a part of the inflow end face of the plugged honeycomb
structure shown in FIG. 2. FIG. 4 is an enlarged plan view of a
part of the outflow end face of the plugged honeycomb structure
shown in FIG. 2. FIG. 5 is a schematic cross-sectional view taken
along the line A-A' of FIG. 3. Furthermore, FIG. 6 is a schematic
perspective view showing a plugged honeycomb segment included in
the plugged honeycomb structure shown in FIG. 1 when viewed from
the inflow-side end face. FIG. 7 is a schematic plan view showing
the plugged honeycomb segment included in the plugged honeycomb
structure shown in FIG. 1 when viewed from the inflow-side end
face. FIG. 8 is a schematic plan view showing the plugged honeycomb
segment included in the plugged honeycomb structure shown in FIG. 1
when viewed from the outflow-side end face.
As shown in FIGS. 6 through 8, a honeycomb segment 4 includes
porous partition walls 1 that define a plurality of cells 2
extending from an inflow end face 11 into which a fluid flows to an
outflow end face 12 from which a fluid flows, and a segment
circumferential wall 3 disposed at the outermost circumference. As
shown in FIGS. 1 through 5, the plugged honeycomb structure 100 of
the present embodiment includes a plurality of the honeycomb
segments 4, and the side surfaces of the plurality of honeycomb
segments 4 are bonded to each other via the bonding layer 6. In the
plugged honeycomb structure 100 of the present embodiment,
honeycomb segments 4 among the plurality of honeycomb segments 4
that are disposed in a center part and are not in contact with the
outer wall 8 have a prismatic columnar shape, where the direction
from the inflow end face 11 to the outflow end face 12 is the axial
direction. Honeycomb segments 4 among the plurality of honeycomb
segments 4 that are disposed in the circumferential part in contact
with the outer wall 8 are formed into a pillar shape, in which a
part of the honeycomb segment 4 which is formed into a prismatic
columnar shape is ground to follow the shape of the outer wall
8.
The bonding layer 6 is prepared by a bonding material to bond the
side surfaces of the plurality of honeycomb segments 4 to each
other. A bonded member obtained by bonding the plurality of
honeycomb segments 4 via the bonding layer 6 may be called a
honeycomb-segment bonded member 7.
The plugging portions 5 are disposed in the open ends of the cells
2 formed in each of the honeycomb segments 4, and they plug either
one of the open end on the side of the inflow end face 11 and the
open end on the side of the outflow end face 12. That is, the
plugging portions 5 are disposed in the open ends of predetermined
cells 2x in the inflow end face 11 of each of the honeycomb
segments 4 and in the open ends of residual cells 2y other than the
predetermined cells 2x in the outflow end face 12 of each of the
honeycomb segments. Hereinafter a cell 2 with the plugging portions
5 disposed in the open end thereof on the inflow end face 11 of
each of the honeycomb segments 4 (i.e., the predetermined cell 2x
as described above) may be called an "outflow cell 2x". Then a cell
2 with the plugging portions 5 disposed in the open end thereof on
the outflow end face 12 of each of the honeycomb segments 4 (i.e.,
the residual cell 2y as described above) may be called an "inflow
cell 2y". A honeycomb segment 4 with the plugging portions 5
disposed in the open ends of the cells 2 may be called a plugged
honeycomb segment 4A.
The honeycomb segment 4 is configured so that cells having at least
two kinds of different shapes are formed in a cross section
orthogonal to the extension direction of the cells 2. For example,
the honeycomb segment 4 shown in FIGS. 6 through 8 includes cells 2
of two kinds of different shapes, whose shape of cell is a
quadrangular shape (e.g., outflow cells 2x) and a pentagonal shape
(e.g., inflow cells 2y). Hereinafter the shape of the cells 2 in a
cross section orthogonal to the extension direction of the cells 2
may be called a "cell shape", a "cross-sectional shape" and a
"shape of a cross section".
In the plugged honeycomb structure 100 of the present embodiment, a
thickness of the segment circumferential wall 3 of each of the
honeycomb segments 4 is from 0.3 to 1.0 mm, and a thickness of the
bonding layer 6 from 0.5 to 1.5 mm.
The honeycomb segment 4 has a center region 18 including a center
of the cross section orthogonal to the extension direction of the
cells 2 and a circumferential region 19 positioned in the side of
the circumference of the center region 18. In FIGS. 7 and 8, the
center region 18 of the honeycomb segment 4 is inside the region
surrounded by the dotted line (i.e., the region indicated with
reference numeral 18). The circumferential region 19 of the
honeycomb segment 4 is outside the region surrounded by the dotted
line (i.e., the region indicated with reference numeral 19).
Furthermore, the cells 2 formed in the center region 18 may be
called center region cells 2a. The cells 2 formed in the
circumferential region 19 may be called circumferential region
cells 2b.
The honeycomb segment 4 has a repeated pattern 9 including a cell
arrangement in which inflow cells 2y surround one outflow cell 2x
in the inflow end face 11. Then, the range including repeating
units 10 to maintain this repeated pattern 9 is the center region
18 as described above. Then the circumferential region 19 is
outside the center region 18, which does not have "repeating units
10 to maintain this repeated pattern 9" as described above. The
"repeated pattern 9" is a pattern configured by a part or all of
the inflow cells 2y which surrounds one outflow cell 2x positioned
at the center, where two or more of the substantially the same
patterns are present in the inflow end face 11 of the honeycomb
segment 4. For example, in the honeycomb segment 4 shown in FIGS. 6
through 8, the plugging portions 5 are disposed so that inflow
cells 2y that a shape of cells 2 is a pentagonal shape surround an
outflow cell 2x that a shape of cells 2 is a quadrangular shape.
With this configuration, the center region 18 has a cell
arrangement such that the inflow cells 2y surround the outflow cell
2x. Then, the "repeated pattern 9" in the honeycomb segment 4 shown
in FIGS. 6 through 8 is the range configured by one outflow cell 2x
and a half of each of the eight inflow cells 2y, i.e., the
"quadrangle surrounded by the dotted line" indicated with reference
numeral 9 of FIGS. 6 through 8. The "repeating units 10 to maintain
the repeated pattern 9" refers to the minimum repeating unit when
the "repeated pattern 9" further includes repeating units. That is,
as shown in FIG. 9, repeating units ("triangles surrounded by the
dotted line" indicated with reference numeral 10 of FIG. 9) are
present in the "repeated pattern 9", which are eight equal parts
obtained by dividing the repeated pattern 9 so as to draw virtual
lines radially from the center of the repeated pattern 9. Such
triangular repeating units 10 are the repeating units 10 to
maintain the repeated pattern 9. The repeating units 10 refer to
the units actually forming a part of the repeated pattern 9.
Therefore, even if a unit of the same shape as that of the
repeating unit 10 does not form a part of the repeated pattern 9,
such a unit is not the "repeating unit 10 to maintain the repeated
pattern 9".
The "inflow cells 2y surround an outflow cell 2x" means the
following configuration in a cross section orthogonal to the
extension direction of the cells 2. The following describes an
example where the cell shape of the outflow cells 2x is a
quadrangular shape as shown in FIGS. 6 through 8. Firstly one side
of an inflow cell 2y is arranged to be adjacent to each of the four
sides of one outflow cell 2x. In this case, one side of each of two
or more inflow cells 2y may be arranged to be adjacent to one side
of one outflow cell 2x. That is, one side of one of the inflow
cells 2y may be arranged to be adjacent to one side of the one
outflow cell 2x at the position of a half of the one side, and then
one side of another inflow cell 2y may be arranged to be adjacent
to the one side of the one outflow cell 2x at the position of the
remaining half of the one side. Then all of the inflow cells 2y
adjacent to the one outflow cell 2x are disposed so that these
inflow cells 2y are adjacent to each other at their mutual one
sides. The geometry of the inflow cells 2y in such a state refers
to the "inflow cells 2y surround an outflow cell 2x".
In the plugged honeycomb structure 100 of the present embodiment,
at least one honeycomb segment 4 (specifically a plugged honeycomb
segment 4A) is configured as follows. In the inflow end face 11 of
the honeycomb segment 4, the circumferential region 19 is
configured to have an open frontal area that is larger than an open
frontal area of the center region 18. The plugged honeycomb
structure 100 of the present embodiment can be preferably used as a
trapping filter to remove a particulate matter included in an
exhaust gas. Then, the thus configured plugged honeycomb structure
can improve a continuous regeneration performance and so can
prevent a segregation of a particulate matter in the filter. That
is, the plugged honeycomb structure 100 of the present embodiment
allows an exhaust gas to flow through the circumferential part of
the honeycomb segment easily even when a lot of PM is accumulated
at the circumferential part of the honeycomb segment. Therefore,
the PM is trapped and it can be excellently burnt at the same time.
Especially in a conventional plugged honeycomb structure having a
segmented structure, the "arrangement of cells (in other words,
continuity of the repeating units of cells)" among the honeycomb
segments of a honeycomb-segment bonded member has not been seen as
a problem especially. Then, it has been considered that, in a
conventional plugged honeycomb structure having a segmented
structure, the center part and the circumferential part of a
honeycomb segment preferably have the same degree of an open
frontal area, and it does not have the configuration where the open
frontal area in the circumferential part is made larger
intentionally. Hereinafter a honeycomb segment configured so that,
in the inflow end face 11 of the honeycomb segment 4, the
circumferential region 19 has an open frontal area that is larger
than an open frontal area of the center region 18 may be called a
"specific honeycomb segment".
As shown in FIGS. 6 through 8, the inflow cells 2y formed in the
honeycomb segment 4 have an apparent cross-sectional shape
orthogonal to the center axial direction of the inflow cells 2y
that is a substantially pentagon. Then, the outflow cells 2x formed
in the honeycomb segment 4 have an apparent cross-sectional shape
orthogonal to the center axial direction of the outflow cells 2x
that is a substantially square. Herein, the "cross-sectional shape"
refers to a shape appearing in the cross section when the cells 2
are cut along a plane orthogonal to the center axial direction, and
refers to the shape of a part surrounded with the partition wall 1
defining the cells 2. The honeycomb segment 4 shown in FIGS. 6
through 8 is configured so that the outflow cells 2x having a
substantially square cross-sectional shape have a relatively larger
cross-sectional area than that of the inflow cells 2y having a
substantially pentagonal cross-sectional shape. In the
circumferential region 19 of the plugged honeycomb segment 4A, it
is configured that the existing ratio of the outflow cells 2x ,
which have a relatively large cross-sectional area, is high. Then
the plugged honeycomb segment 4A is configured so that, in the
inflow end face 11, the circumferential region 19 has open frontal
area that is larger than open frontal area of the center region
18.
As shown in FIGS. 1 through 5, when the plugged honeycomb structure
100 includes a plurality of honeycomb segments 4, it includes
honeycomb segments 4 disposed in a center part that is not in
contact with the outer wall 8 and honeycomb segments 4 that are in
contact with the outer wall 8. Hereinafter, the honeycomb segments
4 disposed in a center part that is not in contact with the outer
wall 8 are called center segments, and the honeycomb segments 4
that are in contact with the outer wall 8 are called
circumferential segments. In the plugged honeycomb structure 100 of
the present embodiment, at least one center segment is preferably a
specific honeycomb segment, and all of the center segments are
specific honeycomb segments more preferably. As described above, in
a specific honeycomb segment, a thickness of the segment
circumferential wall 3 of the honeycomb segment is from 0.3 to 1.0
mm. The plugged honeycomb structures 100 shown in FIGS. 1 through 5
show examples where all of the center segments are specific
honeycomb segments.
The honeycomb segment 4 is preferably configured so that a
predetermined repeated pattern includes cells 2 having at least two
kinds of different shapes. The cell arrangements of the honeycomb
segment 4 shown in FIGS. 6 through 8 include a predetermined
repeated pattern.
In the present specification, the open frontal area in the center
region 18 can be obtained by the following method. Firstly, the
area of the center region 18 in the inflow end face 11 of the
honeycomb segment 4 is obtained. The center region 18 has the
following repeated pattern. The repeated pattern includes cell
arrangement in which inflow cells 2y surround one outflow cell 2x.
Then the center region 18 is the range configured by the repeating
units to maintain the repeated pattern as described above. The area
of the center region 18 can be obtained by a known method, such as
an image analysis. Herein the area of the center region 18 includes
the area of the partition wall 1, the area of the plugging portions
5 disposed in the open ends of the outflow cells 2x and the area of
the open ends of the inflow cells 2y (open end area) existing in
the center region 18 of the inflow end face 11. Next, the open end
area of the inflow cells 2y formed in the center region 18 of the
inflow end face 11 is obtained. The open end area of the inflow
cells 2y formed in the center region 18 of the inflow end face 11
can be obtained by a known method, such as an image analysis. Then,
the percentage of the value obtained by dividing the open end area
S1 of the inflow cells 2y formed in the center region 18 of the
inflow end face 11 by the area S2 of the center region 18
(S1/S2.times.100) is the open frontal area of the center region
18.
In the present specification, the open frontal area in the
circumferential region 19 can be obtained by the following method.
Firstly, the area of the circumferential region 19 in the inflow
end face 11 of the honeycomb segment 4 is obtained. The
circumferential region 19 is outside the center region 18, which
does not include the repeating units 10 to maintain the repeated
pattern 9. The area of the circumferential region 19 can be
obtained by a known method, such as an image analysis. Herein the
area of the circumferential region 19 can be referred to the area
obtained by subtracting the area of the center region 18 from the
overall area of the inflow end face 11 of the honeycomb segment 4.
Next, the open end area of the inflow cells 2y formed in the
circumferential region 19 of the inflow end face 11 is obtained.
The open end area of the inflow cells 2y formed in the
circumferential region 19 of the inflow end face 11 can be obtained
by a known method, such as an image analysis. Then, the percentage
of the value obtained by dividing the open end area S3 of the
inflow cells 2y formed in the circumferential region 19 of the
inflow end face 11 by the area S4 of the circumferential region 19
(S3/S4.times.100) is the open frontal area of the circumferential
region 19.
The value obtained by subtracting the value of the open frontal
area in the center region (the value of percentage) from the value
of the open frontal area in the circumferential region (the value
of percentage) is preferably 10% or more, more preferably 15% or
more and further preferably 20% or more. Although the upper limit
of the value obtained by subtracting the value of the open frontal
area in the center region from the value of the open frontal area
in the circumferential region is not limited especially, the upper
limit may be 40%, for example. If the value obtained by subtracting
the value of the open frontal area in the center region from the
value of the open frontal area in the circumferential region is
less than 10%, a difference between the open frontal area in the
circumferential region and the open frontal area in the center
region becomes small, which may lead to the difficulty to obtain a
sufficient improvement of the continuous regeneration
performance.
The overall shape of the plugged honeycomb structure 100 is not
limited especially. For example, the overall shape of the plugged
honeycomb structure 100 shown in FIG. 1 is a round-pillar shape
where the shape of the inflow end face 11 and the outflow end face
12 are circular. Although an overall shape is not shown, the
overall shape of the plugged honeycomb structure may be a pillar
shape, where the shape of the inflow end face and the outflow end
face are substantially circular in shape, including an ellipse, a
race-track shape, or an oval. Alternatively, the overall shape of
the plugged honeycomb structure may be a polygonal prismatic
columnar shape, where the shape of the inflow end face and the
outflow end face are a quadrangle, a hexagon or the like.
The material of the honeycomb segments is not limited especially,
and main components preferably include various kinds of ceramics,
such as oxides and non-oxides, and metals from the viewpoints of
strength, heat resistance, durability and the like. Specifically,
examples of the ceramics include cordierite, mullite, alumina,
spinel, silicon carbide, silicon nitride, and aluminum titanate.
Examples of the metals include Fe--Cr--Al based metals and metal
silicon. A main component preferably includes one kind or two kinds
or more selected from these materials. Particularly, a main
component preferably includes one kind or two kinds or more
selected from the group consisting of alumina, mullite, aluminum
titanate, cordierite, silicon carbide, and silicon nitride from the
viewpoints of high strength and high heat resistance. Silicon
carbide or silicon-silicon carbide composite materials are
particularly suitable from the viewpoints of high heat conductivity
and high heat resistance. Herein, the "main component" means a
component included in 50 mass % or more of the honeycomb segments,
more preferably 70 mass % or more and further preferably 80 mass %
or more.
The material of the plugging portions is not limited especially.
The material of the plugging portions preferably includes one kind
or two kinds or more selected from the various kinds of ceramics
and metals described above for the suitable materials of the
honeycomb segment.
The plugged honeycomb structure of the present embodiment includes
a plurality of honeycomb segments (specifically plugged honeycomb
segments) that are bonded to each other via the bonding layer. Such
a configuration allows a thermal stress applied to the plugged
honeycomb structure to be distributed, and cracks due to local
temperature rise to be prevented effectively.
The size and the shape of the honeycomb segments are not limited
especially. Note here that if the size of one honeycomb segment is
too large, a sufficient effect of preventing cracks, which is an
advantageous effect of the segment structure, may not be obtained.
If the size of one honeycomb segment is too small, the bonding of
the honeycomb segments with the bonding layer may be
complicated.
The shape of the honeycomb segments is not limited especially. For
example, examples of the shape of the honeycomb segments include a
polygonal prismatic columnar shape, where the cross-sectional shape
orthogonal to the axial direction of the honeycomb segment is a
quadrangle, a hexagon or the like. Honeycomb segments disposed at
the outermost circumference of the plugged honeycomb structure may
have a prismatic columnar shape, a part of which is processed by
grinding or the like in accordance with the overall shape of the
plugged honeycomb structure.
Each of the honeycomb segments 4 in the plugged honeycomb structure
100 of the present embodiment has a repeated pattern including cell
arrangement such that eight inflow cells 2y having a substantially
pentagonal cross-sectional shape surround one outflow cell 2x
having a substantially square cross-sectional shape. By this
configuration, the plugged honeycomb structure 100 of the present
embodiment can make a filtration area of each honeycomb segment 4
larger than the conventional plugged honeycomb structures when they
are used as a filter. Therefore a pressure loss can be reduced
after the PM is accumulated. Further, in the thus configured
honeycomb segment 4, the outflow cells 2x are not adjacent to each
other, and the outflow cells 2x are surrounded entirely with the
inflow cells 2y. This can increase the open frontal area of the
outflow cells 2x, and can decrease the number of the outflow cells
2x compared with the number of the inflow cells 2y , so that the
pressure loss during the initial stage of the operation of the
plugged honeycomb structure 100 can be reduced.
Furthermore, as shown in FIGS. 1 through 5, the inflow cells 2y
having a substantially pentagonal cross-sectional shape are not a
regular pentagon in shape, but preferably have a so-called home
plate shape, for example, whose inner angles are 90.degree.,
135.degree., 90.degree., 90.degree., and 135.degree. that are
clockwise from one vertex. By this configuration, four inflow cells
2y are formed adjacent to each other so that corner portions at the
side of the tip ends of the home plate shapes are collected. In the
four inflow cells 2y where corner portions at their tip ends of the
home plate shapes are collected, two partition walls 1 are mutually
composed perpendicularly. Therefore, a heat capacity at the
partition walls 1 at the part of the collected corner portions can
be kept high, and so a thermal stress can be absorbed when a PM is
burnt.
As shown in FIG. 9, the distance P between the partition wall 1
defining a first side 13 of an outflow cell 2x and the partition
wall 1 defining a second side 14 opposed to the first side 13 of
the outflow cell 2x is preferably in the range of exceeding 0.8 mm
and less than 2.4 mm. Herein, the distance P refers to the shortest
distance connecting the center in the thickness direction of the
partition wall 1 defining the first side 13 and the center in the
thickness direction of the partition wall 1 defining the second
side 14 opposed thereto. Furthermore, as shown in FIG. 9, the
distance Q refers to the distance between the partition wall 1
defining a third side 15 of the inflow cell 2y that is adjacent
substantially parallel to one side of the outflow cell 2x and the
partition wall 1 defining a fourth side 16 opposed to the third
side 15 of the inflow cell 2y. Then the ratio of the distance Q to
the distance P is preferably in the range of exceeding 0.4 and less
than 1.1. Herein, the distance Q refers to the shortest distance
connecting the center in the thickness direction of the partition
wall 1 defining the third side 15 and the center in the thickness
direction of the partition wall 1 defining the fourth side 16
opposed thereto. The relationship between the distance P and the
distance Q in the above range is preferable because it allows a
pressure loss to be reduced while having a good balance during the
initial stage and after the PM accumulation to be reduced while
having good balance. FIG. 9 is a schematic partially enlarged view
of the plugged honeycomb structure that is the first embodiment of
the present invention when viewed from the side of the inflow end
face of the plugged honeycomb structure.
A thickness of the segment circumferential wall of each of the
honeycomb segments is preferably from 0.3 to 1.0 mm, more
preferably from 0.3 to 0.8 mm, and particularly preferably from 0.4
to 0.6 mm. If the thickness of the segment circumferential wall of
each of the honeycomb segments is less than 0.3 mm, it is not
desirable that the strength of the honeycomb segments deteriorates.
If the thickness of the segment circumferential wall of each of the
honeycomb segments exceeds 1.0 mm, it is not desirable that a
pressure loss increases.
A thickness of the bonding layer is preferably from 0.5 to 1.5 mm,
more preferably from 0.7 to 1.3 mm, and particularly preferably
from 0.8 to 1.2 mm. If the thickness of the bonding layer is less
than 0.5 mm, it is not desirable that the PM accumulation limit may
deteriorate. If the thickness of the bonding layer exceeds 1.5 mm,
it is not desirable that a pressure loss may increase.
Furthermore, in the plugged honeycomb structure of the present
embodiment, the cells formed in the center region (center region
cells 2a) preferably include two kinds or more of cells that are
different in cross-sectional shape. In the plugged honeycomb
structure 100 shown in FIGS. 1 through 5, the outflow cells 2x
having a substantially square cross-sectional shape are the center
region cells 2a having a first cross-sectional shape, and the
inflow cells 2y having a substantially pentagonal cross-sectional
shape are the center region cells 2a having a second
cross-sectional shape. By this configuration, the cells having at
least two kinds or more of cross-sectional shapes preferably form a
predetermined repeated pattern. When the cells have a polygonal
cross-sectional shape, the corner portions of the polygon may have
a curved shape having R. For example, a substantial square is the
inclusive term of a square cross-sectional shape and a square
cross-sectional shape having at least one corner portion that is a
curved shape having R. Similarly a substantial pentagon is the
inclusive term of a pentagonal cross-sectional shape and a
pentagonal cross-sectional shape having at least one corner portion
that is a curved shape having R.
A thickness of the partition wall 1 is not limited especially. For
example, the thickness of the partition wall 1 that is present
between one side of one of the cells 2 and one side of another cell
2 adjacent substantially parallel to the one cell 2 is preferably
from 0.07 to 0.51 mm, more preferably from 0.10 to 0.46 mm and
particularly preferably from 0.12 to 0.38 mm. If the thickness of
the partition wall 1 is smaller than 0.07 mm, it is not desirable
that this might cause the difficulty to form the honeycomb segments
4. If the thickness of the partition wall 1 is larger than 0.51 mm,
this is not desirable from the viewpoints of acquiring enough
filtration area and reducing a pressure loss.
In the plugged honeycomb structure of the present embodiment, one
of the suitable examples includes each of the honeycomb segments
having the following configuration. In the inflow cells 2y, a
geometrical surface area GSA is preferably from 10 to 30
cm.sup.2/cm.sup.3, and more preferably from 12 to 18
cm.sup.2/cm.sup.3. The "geometrical surface area GSA" as described
above refers to a value (S/V) obtained by dividing the overall
inner surface area (S) of the inflow cells 2y by the total volume
(V) of the honeycomb segment. Since a larger filtration area of a
filter typically leads to a decrease in a thickness of a PM
accumulated at the partition wall, falling within such a numerical
range of the geometrical surface area GSA allow the pressure loss
of the plugged honeycomb structure to be low. Therefore, if the
geometrical surface area GSA of the inflow cells 2y is smaller than
10 cm.sup.2/cm.sup.3, it is not desirable that this might cause an
increase in a pressure loss during a PM accumulation. If it is
larger than 30 cm.sup.2/cm.sup.3, it is not desirable that this
might cause the pressure loss at the initial stage to increase.
In the plugged honeycomb structure of the present embodiment, a
cell open frontal area of the inflow cells 2y is preferably from 20
to 70%, and more preferably from 25 to 65%. If the cell open
frontal area of the inflow cells 2y is smaller than 20%, it is not
desirable that this might cause the pressure loss at the initial
stage to increase. If it is larger than 70%, it is not desirable
that this might cause the filtration rate to increase, which leads
to a deterioration in a trapping efficiency of a PM, and further
the strength of the partition wall 1 may deteriorate. The "cell
cross-sectional open frontal area of the inflow cells 2y" refers to
the ratio of "the total cross-sectional area of the inflow cells
2y" to the sum of "the cross-sectional area of the entire partition
wall 1 formed in the plugged honeycomb structure" and "the total
cross-sectional area of all of the cells 2" in a cross section
perpendicular to the center axial direction of the plugged
honeycomb structure.
In the plugged honeycomb structure of the present embodiment, a
hydraulic diameter of each of the plurality of cells 2 is
preferably from 0.5 to 2.5 mm, and more preferably from 0.8 to 2.2
mm. If the hydraulic diameter of each of the plurality of cells 2
is smaller than 0.5 mm, it is not desirable that this may cause the
initial pressure loss to increase. If the hydraulic diameter of
each of the plurality of cells 2 is larger than 2.5 mm, it is not
desirable that this may cause a contact area of an exhaust gas with
the partition wall 1 to decrease, and the purification efficiency
may deteriorate. Herein, the hydraulic diameter of each of the
plurality of cells 2 refers to a value calculated by
"4.times.(cross-sectional area)/(circumferential length)" based on
the cross-sectional area and the circumferential length of each
cell 2. The cross-sectional area of the cell 2 refers to the area
of the shape of cell (cross-sectional shape) appearing in a cross
section perpendicular to the center axial direction of the plugged
honeycomb structure, and the circumferential length of the cell
refers to the length of the circumference of the cross-sectional
shape of the cell (length of a closed line surrounding the cross
section).
Considering the trade-off among the initial pressure loss, the
pressure loss during a PM accumulation and the trapping efficiency,
the plugged honeycomb structure of the present embodiment
preferably satisfies the following configurations at the same time.
That is, a geometrical surface area GSA of the inflow cells 2y is
from 10 to 30 cm.sup.2/cm.sup.3, a cell open frontal area of the
inflow cells 2y is from 20 to 70%, and a hydraulic diameter of each
of the plurality of cells 2 is from 0.5 to 2.5 mm, which are
preferably satisfied at the same time. Furthermore, the followings
are more preferably satisfied at the same time, i.e., a geometrical
surface area GSA of the inflow cells 2y is from 12 to 18
cm.sup.2/cm.sup.3, a cell open frontal area of the inflow cells 2y
is from 25 to 65%, and a hydraulic diameter of each of the
plurality of cells 2 is from 0.8 to 2.2 mm.
In the plugged honeycomb structure of the present embodiment, a
catalyst may be loaded onto the partition wall 1 defining the
plurality of cells 2. Loading a catalyst onto the partition wall 1
means that the surface of the partition wall 1 and the inner wall
of pores formed at the partition wall 1 are coated with the
catalyst. Examples of the kinds of catalyst include an SCR catalyst
(zeolite, titania, vanadium), at least two kinds of noble metals of
Pt, Rh, and Pd, and three-way catalyst containing at least one kind
of alumina, ceria, and zirconia. Loading such a catalyst onto the
partition wall enables a detoxication of NOx, CO, HC and the like
contained in an exhaust gas emitted from a direct injection type
gasoline engine and a diesel engine, for example, and facilitates a
combustion of the PM accumulated at the surface of the partition
wall 1 for removal due to the catalyst action.
The method for loading of such catalyst in the plugged honeycomb
structure of the present embodiment is not limited especially, and
a method typically performed by a person skilled in the art can be
used. Specifically, the method for loading of a catalyst includes a
method that a catalyst slurry may be wash-coated, be dried and
fired, for example.
The following describes other embodiments (the second embodiment to
the sixth embodiment) of the plugged honeycomb structure of the
present invention. The plugged honeycomb structures of the second
embodiment to the sixth embodiment are preferably configured
similarly to the first embodiment other than that the plugged
honeycomb segments thereof are different from the plugged honeycomb
segments included in the plugged honeycomb structure of the first
embodiment. FIG. 10 is a schematic plan view showing the plugged
honeycomb segment included in the plugged honeycomb structure that
is the second embodiment of the present invention when viewed from
the inflow-side end face. FIG. 11 is a schematic plan view showing
the plugged honeycomb segment included in the plugged honeycomb
structure that is the third embodiment of the present invention
when viewed from the inflow-side end face. FIG. 12 is a schematic
plan view showing the plugged honeycomb segment included in the
plugged honeycomb structure that is the fourth embodiment of the
present invention when viewed from the inflow-side end face. FIG.
13 is a schematic plan view showing the plugged honeycomb segment
included in the plugged honeycomb structure that is the fifth
embodiment of the present invention when viewed from the
inflow-side end face. FIG. 14 is a schematic plan view showing the
plugged honeycomb segment included in the plugged honeycomb
structure that is the sixth embodiment of the present invention
when viewed from the inflow-side end face.
The plugged honeycomb structure of the second embodiment includes a
plugged honeycomb segment 24A as shown in FIG. 10. The honeycomb
segment 24 includes porous partition walls 21 that define a
plurality of cells 22, and a segment circumferential wall 23
disposed at the outermost circumference. Plugging portions 25 are
disposed in the open ends of outflow cells 22x and in open ends of
inflow cells 22y of the honeycomb segment 24. In FIG. 10, a
reference numeral 22a denotes a center region cell, and a reference
numeral 22b denotes a circumferential region cell.
The honeycomb segment 24 has a center region 38 including a center
of the cross section orthogonal to the extension direction of the
cells 22 and a circumferential region 39 located in the side of the
circumference of the center region 38. In FIG. 10, the inside
region surrounded by the dotted line (i.e., the region indicated by
a reference numeral 38) is the center region 38 of the honeycomb
segment 24. Then the outer region outside of the region surrounded
by the dotted line (i.e., the region indicated by a reference
numeral 39) is the circumferential region 39 of the honeycomb
segment 24. The honeycomb segment 24 has a repeated pattern 29
including the cell arrangement in which inflow cells 22y surround
one outflow cell 22x in the inflow end face 31. The range
configured by repeating units 30 to maintain this repeated pattern
29 is the center region 38 as described above. In the honeycomb
segment 24 shown in FIG. 10, the plugging portions 25 are disposed
so that inflow cells 22y that the shape of the cells 22 is a
pentagonal shape surround one outflow cell 22x that the shape of
the cell 22 is a quadrangular shape. In the inflow end face 31 of
the honeycomb segment 24, the circumferential region 39 is
configured to have an open frontal area that is larger than an open
frontal area of the center region 38.
The plugged honeycomb segment 24A is configured so that a thickness
of the segment circumferential wall 23 of the honeycomb segments 24
is from 0.3 to 1.0 mm. Then, in the plugged honeycomb structure
including this plugged honeycomb segment 24A, a thickness of the
bonding layer 6 is from 0.5 to 1.5 mm.
The plugged honeycomb structure of the third embodiment includes a
plugged honeycomb segment 44A as shown in FIG. 11. The honeycomb
segment 44 includes porous partition walls 41 that define a
plurality of cells 42, and a segment circumferential wall 43
disposed at the outermost circumference. Plugging portions 45 are
disposed in the open ends of outflow cells 42x and in open ends of
inflow cells 42y of the honeycomb segment 44. In FIG. 11, a
reference numeral 42a denotes a center region cell, and a reference
numeral 42b denotes a circumferential region cell.
The honeycomb segment 44 has a center region 58 including a center
of the cross section orthogonal to the extension direction of the
cells 42 and a circumferential region 59 located in the side of the
circumference of the center region 58. In FIG. 11, the inside
region surrounded by the dotted line (i.e., the region indicated by
a reference numeral 58) is the center region 58 of the honeycomb
segment 44. Then the outer region outside of the region surrounded
by the dotted line (i.e., the region indicated by a reference
numeral 59) is the circumferential region 59 of the honeycomb
segment 44. The honeycomb segment 44 has a repeated pattern 49
including the cell arrangement in which inflow cells 42y surround
one outflow cell 42x in the inflow end face 51. The range
configured by repeating units 50 to maintain this repeated pattern
49 is the center region 58 as described above. In the honeycomb
segment 44 shown in FIG. 11, the plugging portions 45 are disposed
so that inflow cells 42y that a shape of the cells 42 is a
pentagonal shape surround one outflow cell 42x that a shape of the
cell 42 is a quadrangular shape. That is, the plugged honeycomb
segment 44A shown in FIG. 11 has the "repeated pattern 49"
including the cell arrangement configured by the outflow cell 42x
whose cross-sectional shape is a quadrangular shape and the inflow
cells 42y whose cross-sectional shape is a pentagonal shape.
In the plugged honeycomb segment 44A shown in FIG. 11 as well, in
the inflow end face 51 of the honeycomb segment 44, the
circumferential region 59 is configured to have an open frontal
area that is larger than an open frontal area of the center region
58.
The plugged honeycomb structure of the fourth embodiment includes a
plugged honeycomb segment 64A as shown in FIG. 12. The honeycomb
segment 64 includes porous partition walls 61 that define a
plurality of cells 62, and a segment circumferential wall 63
disposed at the outermost circumference. Plugging portions 65 are
disposed in the open ends of outflow cells 62x and in the open ends
of inflow cells 62y of the honeycomb segment 64. In FIG. 12, a
reference numeral 62a denotes a center region cell, and a reference
numeral 62b denotes a circumferential region cell.
The honeycomb segment 64 has a center region 78 including a center
of the cross section orthogonal to the extension direction of the
cells 62 and a circumferential region 79 located in the side of the
circumference of the center region 78. In FIG. 12, the inside
region surrounded by the dotted line (i.e., the region indicated by
a reference numeral 78) is the center region 78 of the honeycomb
segment 64. Then the outer region outside of the region surrounded
by the dotted line (i.e., the region indicated by a reference
numeral 79) is the circumferential region 79 of the honeycomb
segment 64. The honeycomb segment 64 has a repeated pattern 69
including the cell arrangement in which inflow cells 62y surround
one outflow cell 62x in the inflow end face 71. The range
configured by repeating units 70 to maintain this repeated pattern
69 is the center region 78 as described above. The plugged
honeycomb segment 64A shown in FIG. 12 has the "repeated pattern
69" including the cell arrangement configured by the outflow cell
62x whose cross-sectional shape is an octagonal shape and the
inflow cells 62y whose cross-sectional shape is a quadrangular
shape and an octagonal shape.
In the plugged honeycomb segment 64A shown in FIG. 12 as well, in
the inflow end face 71 of the honeycomb segment 64, the
circumferential region 79 is configured to have an open frontal
area that is larger than an open frontal area of the center region
78.
The plugged honeycomb structure of the fifth embodiment includes a
plugged honeycomb segment 84A as shown in FIG. 13. The honeycomb
segment 84 includes porous partition walls 81 that define a
plurality of cells 82, and a segment circumferential wall 83
disposed at the outermost circumference. Plugging portions 85 are
disposed in the open ends of outflow cells 82x and in open ends of
inflow cells 82y of the honeycomb segment 84. In FIG. 13, a
reference numeral 82a denotes a center region cell, and a reference
numeral 82b denotes a circumferential region cell.
The honeycomb segment 84 has a center region 98 including a center
of the cross section orthogonal to the extension direction of the
cells 82 and a circumferential region 99 located in the side of the
circumference of the center region 98. In FIG. 13, the inside
region surrounded by the dotted line (i.e., the region indicated by
a reference numeral 98) is the center region 98 of the honeycomb
segment 84. Then the outer region outside of the region surrounded
by the dotted line (i.e., the region indicated by a reference
numeral 99) is the circumferential region 99 of the honeycomb
segment 84. The honeycomb segment 84 has a repeated pattern 89
including the cell arrangement in which inflow cells 82y surround
one outflow cell 82x in the inflow end face 91. The range
configured by repeating units 90 to maintain this repeated pattern
89 is the center region 98 as described above. The plugged
honeycomb segment 84A shown in FIG. 13 has the "repeated pattern
89" including the cell arrangement configured by the outflow cell
82x whose cross-sectional shape is an octagonal shape and the
inflow cells 82y whose cross-sectional shape is a quadrangular
shape and an octagonal shape.
In the plugged honeycomb segment 84A shown in FIG. 13 as well, in
the inflow end face 91 of the honeycomb segment 84, the
circumferential region 99 is configured to have an open frontal
area that is larger than an open frontal area of the center region
98.
The plugged honeycomb structure of the sixth embodiment includes a
plugged honeycomb segment 124A as shown in FIG. 14. The honeycomb
segment 124 includes porous partition walls 121 that define a
plurality of cells 122, and a segment circumferential wall 123
disposed at the outermost circumference. Plugging portions 125 are
disposed in the open ends of outflow cells 122x and in the open
ends of inflow cells 122y of the honeycomb segment 124. In FIG. 14,
a reference numeral 122a denotes a center region cell, and a
reference numeral 122b denotes a circumferential region cell.
The honeycomb segment 124 has a center region 138 including a
center of the cross section orthogonal to the extension direction
of the cells 122 and a circumferential region 139 located in the
side of the circumference of the center region 138. In FIG. 14, the
inside region surrounded by the dotted line (i.e., the region
indicated by a reference numeral 138) is the center region 138 of
the honeycomb segment 124. Then the outer region outside of the
region surrounded by the dotted line (i.e., the region indicated by
a reference numeral 139) is the circumferential region 139 of the
honeycomb segment 124. The honeycomb segment 124 has a repeated
pattern 129 including the cell arrangement in which inflow cells
122y surround one outflow cell 122x in the inflow end face 131. The
range configured by repeating units 130 to maintain this repeated
pattern 129 is the center region 138 as described above. In the
honeycomb segment 124 shown in FIG. 14, the plugging portions 125
are disposed so that inflow cells 122y that a shape of the cells
122 is a hexagonal shape surround one outflow cell 122x that a
shape of the cell 122 is a quadrangular shape. That is, the plugged
honeycomb segment 124A shown in FIG. 14 has the "repeated pattern
129" including the cell arrangement configured by the outflow cell
122xwhose cross-sectional shape is a quadrangular shape and the
inflow cells 122y whose cross-sectional shape is a hexagonal
shape.
In the plugged honeycomb segment 124A shown in FIG. 14 as well, in
the inflow end face 131 of the honeycomb segment 124, the
circumferential region 139 is configured to have an open frontal
area that is larger than an open frontal area of the center region
138.
Furthermore, the plugged honeycomb segments in the first to the
sixth embodiments are configured so that the overall cell
arrangement defined by the partition walls is axisymmetric in a
cross section orthogonal to the axial direction of the plugged
honeycomb segment. Although not illustrated, the plugged honeycomb
segment may be configured so that the overall arrangement of the
cells defined by the partition walls is not axisymmetric in a cross
section orthogonal to the axial direction of the plugged honeycomb
segment. In such a plugged honeycomb segment as well, it is
configured so that the circumferential region is configured to have
an open frontal area that is larger than an open frontal area of
the center region in the inflow end face of the honeycomb segment,
whereby advantageous effects in the same as those of the plugged
honeycomb structure of the first embodiment can be obtained.
(2) Method for Manufacturing Plugged Honeycomb Structure:
There is no particular limitation on the method for manufacturing
the plugged honeycomb structure of the present embodiment shown in
FIGS. 1 through 5, and this can be manufactured by the following
method, for example. Firstly a kneaded material having plasticity
is prepared to manufacture a honeycomb segment. The kneaded
material to manufacture a honeycomb segment can be prepared by
appropriately adding additives such as a binder and water into a
material selected as a raw material powder from the aforementioned
materials suitable for honeycomb segment. As the raw material
powder, for example, silicon carbide powder may be used. For
example, the binder includes methylcellulose or
hydroxypropoxylmethylcellulose. Moreover, the additives include a
surfactant.
Next, the thus obtained kneaded material is extruded to prepare a
prismatic columnar honeycomb formed body, having partition walls
defining a plurality of cells and a segment circumferential wall
disposed at the outermost circumference. A plurality of the
honeycomb formed bodies is prepared.
The thus obtained honeycomb formed bodies are dried by microwaves
and hot air, for example, and then open ends of the cells are
plugged with the same material as the material used for the
honeycomb formed bodies to prepare plugging portions. After the
plugging portions are prepared, the honeycomb formed bodies may be
further dried.
Next, each of the honeycomb formed bodies with the plugging
portions is fired to obtain a plugged honeycomb segment. The firing
temperature and the atmosphere for firing depend on the raw
materials used, and a person skilled in the art could select an
appropriate temperature and atmosphere for firing depending on the
selected materials. Next, the plurality of plugged honeycomb
segments are mutually bonded by using a bonding material. After the
plurality of plugged honeycomb segments are dried and hardened, a
circumference is processed to obtain a desirable shape, and then
this can provide a plugged honeycomb structure having a segmented
structure. The bonding material may include a material prepared by
adding a solvent such as water into to a ceramics material to be in
a paste form. Since the cells are exposed in the processed surface
after the circumference of the plugged honeycomb segments is
processed, a circumference coating material may be applied to the
processed surface to form the outer wall as shown in FIG. 1. As the
circumference coating material, the same material as that of the
bonding material can be used.
(3) Plugged Honeycomb Segment:
Next, the following describes the first embodiment of the plugged
honeycomb segment of the present invention. The plugged honeycomb
segment of the present embodiment is used for the plugged honeycomb
structure of the first embodiment as described above.
The plugged honeycomb segment of the present embodiment includes a
honeycomb segment 4 and plugging portions 5 as shown in FIGS. 6
through 8. The honeycomb segment 4 includes porous partition walls
1 that define a plurality of cells 2 extending from an inflow end
face 11 to which a fluid flows to an outflow end face 12 from which
a fluid flows, and a segment circumferential wall 3 disposed at the
outermost circumference. The plugging portions 5 are disposed in
the open ends of the cells 2 formed in each of the honeycomb
segments 4, and they plug either one of the open end on the side of
the inflow end face 11 and on the side of the outflow end face 12.
In the plugged honeycomb segment 4A of the present embodiment, a
thickness of the segment circumferential wall 3 of the honeycomb
segment 4 is from 0.3 to 1.0 mm.
The honeycomb segment 4 has a center region 18 including a center
of the cross section orthogonal to the extension direction of the
cells 2 and a circumferential region 19 located in the side of the
circumference of the center region 18. In FIGS. 7 and 8, the inside
region surrounded by the dotted line (i.e., the region indicated
with a reference numeral 18) is the center region 18 of the
honeycomb segment 4. Then the outer region outside of the region
surrounded by the dotted line (i.e., the region indicated with a
reference numeral 19) is the circumferential region 19 of the
honeycomb segment 4. The honeycomb segment 4 has a repeated pattern
9 including cell arrangement in which inflow cells 2y surround one
outflow cell 2x in the inflow end face 11. Then, the range
including repeating units 10 to maintain this repeated pattern 9 is
the center region 18 as described above. Then the circumferential
region 19 is outside the center region 18, which does not have the
repeating units 10 to maintain this repeated pattern 9. Herein, the
circumferential region 19 may include the units of the same shape
of that of the repeating units 10, which actually do not form a
part of the repeated pattern 9, in the region.
The plugged honeycomb segment 4A of the present embodiment is
configured so that in the inflow end face 11 of the honeycomb
segment 4 the circumferential region 19 has open frontal area that
is larger than open frontal area of the center region 18. The thus
configured plugged honeycomb segment of the present embodiment can
be preferably used as a honeycomb segment to prepare the plugged
honeycomb structure of the first embodiment.
A suitable example of the plugged honeycomb segment of the present
embodiment includes a plugged honeycomb segment used for the
plugged honeycomb structure of the first embodiment.
Other suitable examples of the plugged honeycomb segment of the
present invention include plugged honeycomb segments used for the
plugged honeycomb structures according to the second to the sixth
embodiments shown in FIGS. 10 through 14.
EXAMPLES
Example 1
As a ceramic raw material, silicon carbide (SiC) powder and metal
silicon (Si) powder were mixed at the mass ratio of 80:20 to
prepare a mixed raw material. Hydroxypropylmethylcellulose as a
binder, a water absorbable resin as a pore former and further water
were added to this mixed raw material to prepare a forming raw
material. Then, the obtained forming raw material was kneaded by a
kneader to prepare a kneaded material.
Next, the obtained kneaded material was formed by a vacuum extruder
to prepare sixteen pieces of quadrangular prismatic-columnar
honeycomb segments 4 having a repeated pattern 9 including the same
cell arrangement as that of the plugged honeycomb segment 4A shown
in FIG. 7. Herein, the "same cell arrangement as that of the
plugged honeycomb segment 4A shown in FIG. 7" means the arrangement
of cells such that eight inflow cells whose cross-sectional shape
is a pentagonal shape surround an outflow cell whose
cross-sectional shape is a square shape. Then, the repeated pattern
9 is the range including one outflow cell 2xand a half of each of
eight inflow cells 2y as shown in FIG. 7.
Next, the obtained honeycomb segments were dried by high-frequency
induction heating and then dried at 120.degree. C. for 2 hours by a
hot-air drier. The drying was performed so that the outflow end
faces of the honeycomb segments were in a vertically downward
direction.
Plugging portions were formed in each of the dried honeycomb
segments. Firstly, the inflow end face of the honeycomb segment was
masked, and next the masked end (end on the side of the inflow end
face) was immersed in a plugging slurry, and the plugging slurry
was charged into open ends of the cells which were not masked
(outflow cells). In this way, plugging portions were formed on the
side of the inflow end face of the honeycomb segment. Then,
plugging portions were formed on the side of the outflow end face
at the inflow cells of the dried honeycomb segment in the same
manner as on the side of the inflow end face of the honeycomb
segment.
Then the honeycomb segment including the plugging portions was
degreased and fired to obtain a plugged honeycomb segment. The
degreasing was performed at 550.degree. C. for 3 hours, and the
firing was performed at 1,450.degree. C. in an argon atmosphere for
2 hours. The firing was performed so that the outflow end faces of
the honeycomb segments including plugging portions were in a
vertically downward direction.
The prepared plugged honeycomb segment had the circumferential
region 19 including the triangular inflow cells 2y formed at the
outermost circumference and a half of the pentagonal inflow cells
2y surrounding the quadrangular outflow cells 2x in the same as the
plugged honeycomb segment 4A shown in FIG. 7. Then, the center
region 18 was inside the circumferential region 19. The design of
the plugged honeycomb segment in which the inflow cells and the
outflow cells are configured as described above is called "design
A". In the column of "design" of in table 1, the design of the
plugged honeycomb segment used in Example 1 is shown.
In the prepared plugged honeycomb segment, a cross sectional shape
orthogonal to the axial direction was square, and the length of one
side of the square (segment size) was 37.1 mm. Furthermore, in the
honeycomb segment, the length in the axial direction was 152.4 mm.
Then in the plugged honeycomb segment, the distance P shown in FIG.
7 was 2.0 mm, the distance Q was 1.2 mm, and the thickness of the
partition wall was 0.32 mm. Table 1 shows the values of "segment
size (one side) [mm]", "thickness of partition wall [mm]",
"distance P [mm]", and "distance Q [mm]".
In the prepared plugged honeycomb segment, the open frontal area of
the center region in the inflow end face was 34%. In the prepared
plugged honeycomb segment, the open frontal area of the
circumferential region in the inflow end face was 65%. The value
obtained by subtracting the value of the open frontal area in the
center region from the value of the open frontal area in the
circumferential region in the inflow end face was 31%. Table 1
shows the values of "open frontal area of center region in inflow
end face", "open frontal area of circumferential region in inflow
end face" and "difference of open-frontal area". Herein the
"difference of open-frontal area" refers to a value obtained by
subtracting the value of the open frontal area in the center region
from the value of the open frontal area in the circumferential
region in the inflow end face. In the prepared plugged honeycomb
segment, a thickness of the segment circumferential wall was 0.5
mm. In the column of "segment circumferential wall thickness [mm]"
in Table 1, the thickness of the segment circumferential wall is
shown.
The sixteen pieces of plugged honeycomb segments were fired and
integrally bonded with a bonding material (ceramic cement). The
bonding material contained inorganic particles and an inorganic
adhesive as main components and an organic binder, a surfactant, a
foamable resin, water and the like as subcomponents. Plate-like
particles were used as the inorganic particles, and a colloidal
silica (silica sol) was used as the inorganic adhesive. Mica was
used as the plate-like particles. The circumference of the
honeycomb-segment bonded member including the sixteen pieces of
honeycomb segments integrally bonded was ground to be a round
pillar shape, and a coating material was applied to the
circumferential face thereof to obtain the plugged honeycomb
structure of Example 1. The diameter at the end face of the plugged
honeycomb structure of Example 1 was 143.8 mm. The coating material
contained a ceramic powder, water and a bonding material. The width
of the bonding layer formed with the bonding material was 1 mm. In
the column of "bonding width [mm]" in Table 1, the width of the
bonding layer is shown.
TABLE-US-00001 TABLE 1 Open Thickness Segment Thick- frontal area
Open frontal of size ness of of center area of segment (one
partition Distance Distance region in circumferential Difference
Bonding circum- side) wall P Q inflow end region in inflow of open
width ferential wall Design [mm] [mm] [mm] [mm] face end face
frontal area [mm] [mm] Comp. C 39.4 0.32 2.0 1.2 34% 34% 0% 1 0.5
Ex. 1 Ex. 1 A 37.1 0.32 2.0 1.2 34% 65% 31% 1 0.5 Ex. 2 B 38.2 0.32
2.0 1.2 34% 44% 10% 1 0.5 Ex. 3 C 39.3 0.32 2.0 1.2 34% 35% 1% 1
0.5 Comp. C 39.5 0.32 2.0 1.2 34% 32% -2% 1 0.5 Ex. 2 Ex. 4 A 37.1
0.32 2.0 1.2 34% 65% 31% 1.5 0.5 Comp. A 37.1 0.32 2.0 1.2 34% 65%
31% 1.6 0.5 Ex. 3 Ex. 5 A 37.1 0.32 2.0 1.2 34% 65% 31% 0.5 0.5
Comp. A 37.1 0.32 2.0 1.2 34% 65% 31% 0.4 0.5 Ex. 4 Ex. 6 A 38.1
0.32 2.0 1.2 34% 65% 31% 1 1 Comp. A 38.3 0.32 2.0 1.2 34% 65% 31%
1 1.1 Ex. 5 Ex. 7 A 36.7 0.32 2.0 1.2 34% 65% 31% 1 0.3 Comp. A
36.5 0.32 2.0 1.2 34% 65% 31% 1 0.2 Ex. 6 Ex. 8 C 39.3 0.32 2.0 1.2
34% 35% 1% 1.5 0.5 Comp. C 39.3 0.32 2.0 1.2 34% 35% 1% 1.6 0.5 Ex.
7 Ex. 9 C 39.3 0.32 2.0 1.2 34% 35% 1% 0.5 0.5 Comp. C 39.3 0.32
2.0 1.2 34% 35% 1% 0.4 0.5 Ex. 8 Ex. 10 C 40.3 0.32 2.0 1.2 34% 35%
1% 1 1 Comp. C 40.5 0.32 2.0 1.2 34% 35% 1% 1 1.1 Ex. 9 Ex. 11 C
38.9 0.32 2.0 1.2 34% 35% 1% 1 0.3 Comp. C 38.7 0.32 2.0 1.2 34%
35% 1% 1 0.2 Ex. 10 Comp. E 38.4 0.31 1.7 1.4 45% 45% 0% 1 0.5 Ex.
11 Ex. 12 D 36.2 0.31 1.7 1.4 45% 81% 36% 1 0.5 Ex. 13 E 36.9 0.31
1.7 1.4 45% 55% 10% 1 0.5 Ex. 14 E 38.1 0.31 1.7 1.4 45% 46% 1% 1
0.5
Examples 2 to 14
The plugged honeycomb structures of Examples 2 to 14 were
manufactured, in which the design, segment size, thickness of a
partition wall, distance P, distance Q, open frontal area of a
center region in inflow end face, open frontal area of a
circumferential region in an inflow end face, bonding width, and
segment circumferential wall thickness were changed as shown in
Table 1. The ceramic raw material to prepare the plugged honeycomb
segments was prepared in the same manner as in Example 1.
In Example 2, sixteen pieces of quadrangular prismatic-columnar
honeycomb segments 24 having a repeated pattern 29 including the
same cell arrangement as that of the plugged honeycomb segment 24A
shown in FIG. 10 were prepared. The prepared plugged honeycomb
segment included the two kinds of the quadrangular outflow cells
22x and the pentagonal inflow cells 22y at the outermost
circumference in the same manner as in the plugged honeycomb
segment 24A shown in FIG. 10. The plugged honeycomb segment
prepared in Example 2 had the circumferential region 39 including
the outflow cells 22x and the inflow cells 22y formed at the
outermost circumference as well as a part of the pentagonal inflow
cells 22y formed inwardly by one of the outflow cells 22x formed at
the outermost circumference. Then, the center region 38 was inside
the circumferential region 39. The design of the plugged honeycomb
segment in which the inflow cells and the outflow cells are
configured as described above is called "design B". In the column
of "design" in Table 1, the design of the plugged honeycomb segment
used for Example 2 is shown.
In Example 3, sixteen pieces of quadrangular prismatic-columnar
honeycomb segments 44 having a repeated pattern 49 including the
same cell arrangement as that of the plugged honeycomb segment 44A
shown in FIG. 11 were prepared. The prepared plugged honeycomb
segment included the quadrangular outflow cells 42x and the
quadrangular inflow cells 42y at the outermost circumference in the
same manner as in the plugged honeycomb segment 44A shown in FIG.
11. The plugged honeycomb segment prepared in Example 3 had the
circumferential region 59 and the center region 58 configured as
follows. The circumferential region 59 included the outflow cells
42x and the inflow cells 42y formed at the outermost circumference
as well as the pentagonal inflow cells 42y formed on the outermost
circumferential side and a part of the pentagonal inflow cells 42y
formed inwardly by one of these outflow cells 42x. Then, the center
region 58 was inside the circumferential region 59. The design of
the plugged honeycomb segment in which the inflow cells and the
outflow cells are configured as described above is called "design
C". In the column of "design" in Table 1, the design of the plugged
honeycomb segment used for Example 3 is shown.
In Example 12, sixteen pieces of quadrangular prismatic-columnar
honeycomb segments 84 having a repeated pattern 89 including the
same cell arrangement as that of the plugged honeycomb segment 84A
shown in FIG. 13 were prepared. The prepared plugged honeycomb
segment had the circumferential region 99 including a part of the
inflow cells 82y and the outflow cells 82x formed at the outermost
circumference in the same manner as in the plugged honeycomb
segment 84A shown in FIG. 13. Then, the center region 98 was inside
the circumferential region 99. The design of the plugged honeycomb
segment in which the inflow cells and the outflow cells are
configured as described above is called "design D". In the column
of "design" in Table 1, the design of the plugged honeycomb segment
used for Example 12 is shown.
In Example 13, sixteen pieces of quadrangular prismatic-columnar
honeycomb segments 64 having a repeated pattern 69 including the
same cell arrangement as that of the plugged honeycomb segment 64A
shown in FIG. 12 were prepared. The prepared plugged honeycomb
segment had the circumferential region 79 in the same manner as in
the plugged honeycomb segment 64A shown in FIG. 12. That is, the
circumferential region 79 included the inflow cells 62y and the
outflow cells 62x formed at the outermost circumference as well as
a part of the inflow cells 62y formed inwardly by one of these
inflow cells 62yformed at the outermost circumference. Then, the
center region 78 was inside the circumferential region 79. The
design of the plugged honeycomb segment in which the inflow cells
and the outflow cells are configured as described above is called
"design E". In the column of "design" in Table 1, the design of the
plugged honeycomb segment used for Example 13 is shown.
Comparative Examples 1 to 11
The plugged honeycomb structures of Comparative Examples 1 to 11
were manufactured, in which the design, segment size, thickness of
a partition wall, distance P, distance Q, open frontal area of a
center region at an inflow end face, open frontal area of a
circumferential region at an inflow end face, bonding width, and
segment circumferential wall thickness were changed as shown in
Table 1. The ceramic raw material to prepare the plugged honeycomb
segments was prepared in the same manner as in Example 1.
As to the plugged honeycomb structures of Examples 1 to 14 and
Comparative Examples 1 to 11, evaluations of a regeneration
efficiency, a pressure loss and an isostatic strength were carried
out by methods described below. Table 2 shows the result of the
evaluations.
TABLE-US-00002 TABLE 2 Regeneration efficiency Pressure loss
Isostatic strength Comp. Ex. 1 D -- B Ex. 1 A C B Ex. 2 A C B Ex. 3
C B B Comp. Ex. 2 D B B Ex. 4 A C A Comp. Ex. 3 A D A Ex. 5 A B C
Comp. Ex. 4 A B D Ex. 6 B C A Comp. Ex. 5 B D A Ex. 7 A B C Comp.
Ex. 6 A A D Ex. 8 C C A Comp. Ex. 7 D D A Ex. 9 B A C Comp. Ex. 8 B
A D Ex. 10 C C A Comp. Ex. 9 D D A Ex. 11 B B C Comp. Ex. 10 B A D
Comp. Ex. 11 D B B Ex. 12 A C B Ex. 13 A C B Ex. 14 C B B
(Regeneration Efficiency)
Firstly 20 g/L of platinum/palladium based catalyst for catalyzed
soot filters (CSF) was loaded onto the plugged honeycomb structures
of Examples 1 to 14 and Comparative Examples 1 to 11, and honeycomb
filters with CSF catalyst were prepared. The CSF is the
abbreviation of Catalyzed Soot Filter. Such a honeycomb filter with
CSF catalyst was attached to an exhaust pipe of a diesel engine for
an automobile of a displacement of 2.0 L, and a regeneration test
was performed. The conditions of the regeneration test were as
follows. Firstly, the diesel engine was operated under the
conditions of the engine revolutions of 2,000 rpm and the engine
torque of 60 Nm so as to let 6 g/L of soot accumulate on the
plugged honeycomb structure. Next, the mass of the plugged
honeycomb structure in which a soot was accumulated was measured.
Next, the diesel engine was operated under the conditions of the
engine revolutions of 2,000 rpm and the engine torque of 60 Nm, and
when the temperature of an exhaust gas immediately before flowing
into the plugged honeycomb structure became stable, then a post
injection was performed, and a regeneration was performed for 10
minutes. Thereafter the mass of the plugged honeycomb structure
after the regeneration was measured. Based on a difference in mass
of the honeycomb filter with CSF catalyst between before and after
the test, the amount of soot left in the honeycomb filter with CSF
catalyst was obtained. A regeneration efficiency was evaluated
based on the following evaluation criteria.
Evaluation A: the amount of soot left was less than 0.5 g/L.
Evaluation B: the amount of soot left was 0.5 g/L or more and less
than 1.0 g/L.
Evaluation C: the amount of soot left was 1.0 g/L or more and less
than 1.5 g/L.
Evaluation D: the amount of soot left was 1.5 g/L or more.
(Pressure Loss)
Firstly, the plugged honeycomb structure of Comparative Example 1
was attached to an exhaust system of an automobile which a diesel
engine for automobile of a displacement of 2.0 L was mounted. Using
this automobile, the pressure loss during full-load step-up was
measured in the vehicle testing by a chassis dynamometer.
Specifically, the engine revolutions were raised by 1,000 rpm for
every 3 minutes/step to 5,000 rpm, and the pressure loss at each
step was measured. The pressure loss of the plugged honeycomb
structure of Comparative Example 1 was set as the reference for
pressure loss evaluation. Next, the pressure loss of the plugged
honeycomb structures of Examples 1 to 14 and Comparative Examples 2
to 11 was measured by a method in the same manner as in Comparative
Example 1. The values of pressure loss of these Examples and
Comparative Examples were compared with the value of pressure loss
of Comparative Example 1 as the reference, and the pressure loss
was evaluated based on the following evaluation criteria.
Furthermore, the pressure loss at the engine revolutions of 5,000
rpm was used in the evaluation.
Evaluation A: the ratio to Comparative Example 1 as the reference
was -5% or less.
Evaluation B: the ratio to Comparative Example 1 as the reference
was +5% or less.
Evaluation C: the ratio to Comparative Example 1 as the reference
was +15% or less.
Evaluation D: the ratio to Comparative Example 1 as the reference
exceeded +15%.
(Isostatic Strength)
An isostatic strength was measured in accordance with the isostatic
fracture strength testing specified at M505-87 of the Japanese
Automotive Standards Organization (JASO) that is a specification
issued by the Society of Automotive Engineers of Japan. An
isostatic fracture strength is tested by placing a plugged
honeycomb structure in a rubber-made tubular container, which is
sealed with an aluminum plate, and applying an isostatic pressure
thereto in water. That is, the isostatic fracture strength testing
was performed by measuring the magnitude of a hydraulic pressure at
which the honeycomb part of a plugged honeycomb structure fell into
the hollow and was broken. An isostatic strength measured by this
isostatic fracture strength testing is indicated as a pressure
(MPa) applied when the plugged honeycomb structure breaks down. The
isostatic strength was evaluated based on the following evaluation
criteria.
Evaluation A: isostatic strength was 3.0 MPa or more.
Evaluation B: isostatic strength was 2.0 MPa or more and less than
3.0 MP.
Evaluation C: isostatic strength was 1.0 MPa or more and less than
2.0 MP.
Evaluation D: isostatic strength was less than 1.0 MP.
(Results)
In the plugged honeycomb structures of Examples 1 to 14, all
evaluations of the regeneration efficiency, the pressure loss and
the isostatic strength were Evaluation C or better. On the
contrary, in all of the plugged honeycomb structures of Comparative
Examples 1, 2, 7, 9 and 11, the evaluations of the regeneration
efficiency were Evaluation D. In the plugged honeycomb structures
that a thickness of the bonding layer was 1.6 mm in Comparative
Examples 3 and 7, the evaluations of a pressure loss were
Evaluation D. In the plugged honeycomb structures that a thickness
of the bonding layer was 0.4 mm in Comparative Examples 4 and 8,
the evaluations of the isostatic strength were Evaluation D. In the
plugged honeycomb structures that a thickness of the segment
circumferential wall was 1.1 mm in Comparative Examples 5 and 9,
the evaluations of a pressure loss were Evaluation D. Furthermore,
in the plugged honeycomb structures in Comparative Examples 7 and
9, the evaluations of the regeneration efficiency as well were
Evaluation D. In the plugged honeycomb structures that a thickness
of the segment circumferential wall was 0.2 mm in Comparative
Examples 6 and 10, the evaluations of the isostatic strength were
Evaluation D. Such results show that the plugged honeycomb
structure of Examples 1 to 14 configured so that in the inflow end
face of the honeycomb segment, the circumferential region has open
frontal area that is larger than open frontal area in the center
region were excellent in the regeneration efficiency. It was
confirmed that the thickness of the segment circumferential wall of
0.3 to 1.0 mm and the thickness of the bonding layer of 0.5 to 1.5
mm allow a regeneration efficiency to be raised and as well as a
good pressure loss and a good isostatic strength to obtain.
The plugged honeycomb structure of the present invention can be
used as a trapping filter to remove particulates or the like
included in an exhaust gas emitted from a direct injection type
gasoline engine, a diesel engine and the like. The plugged
honeycomb segment of the present invention can be used to
manufacture the plugged honeycomb structure of the present
invention.
DESCRIPTION OF REFERENCE NUMERALS
1, 21, 41, 61, 81, 121: partition wall
2, 22, 42, 62, 82, 122: cell
2a, 22a, 42a, 62a, 82a, 122a: center region cell
2b, 22b, 42b, 62b, 82b, 122b: circumferential region cell
2x, 22x, 42x, 62x, 82x, 122x: outflow cell (predetermined cell)
2y, 22y, 42y, 62y, 82y, 122y: inflow cell (residual cell)
3, 23, 43, 63, 83, 123: segment circumferential wall
4, 24, 44, 64, 84, 124: honeycomb segment
4A, 24A, 44A, 64A, 84A, 124A; plugged honeycomb segment
5, 25, 45, 65, 85, 125: plugging portion
6: bonding layer
7: honeycomb-segment bonded member
8: outer wall
9, 29, 49, 69, 89, 129: repeated pattern
10, 30, 50, 70, 90, 130: repeating unit
11, 31, 51, 71, 91, 131: inflow end face
12: outflow end face
13: first side
14: second side
15: third side
16: fourth side
18, 38, 58, 78, 98, 138: center region
19, 39, 59, 79, 99, 139: circumferential region
100: plugged honeycomb structure
P, Q: distance
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